Mobile phone cellular network operators seek to foster fixed to mobile substitution, in which users are encouraged to switch from a fixed cable or wire Digital Subscriber Line (DSL) to a mobile network. One way of encouraging substitution is by offering users Home Zone services, where phone calls and data services are much cheaper when the user is in their Home Zone cell than in other cells. Home Zone services for voice calls are becoming popular with some operators (e.g., O2's Genion™ service in Germany). A key prerequisite is to offer the service such that it really ‘emulates’ the fixed service (e.g., Genion users are allocated both a mobile number and a fixed number). Callers to the fixed number pay standard fixed network call rates. Genion subscribers can choose what happens to calls to their fixed number when they are outside their Home Zones: calls can be forwarded to voicemail for free or to the mobile number for an additional fee.
Today, the availability of a Home Zone service depends on the coverage of 3G networks (voice Home Zone can be offered using 2G networks as well). However, many subscribers opt to keep their fixed lines because these are used for Internet access. When it comes to Internet access, the capabilities of mobile networks are still far behind that of DSL or cable networks. While achievable data rates are comparable with average-speed DSL, cell capacities are limited, which makes providing Internet access over mobile networks relatively expensive for the mobile network operator. Operators hope that with High Speed Packet Access (HSPA) technology they can become a true competitor of DSL operators, but analysis shows that the possibilities of this are still limited.
One reason for this is that, in contrast with access to DSL systems, in a mobile network the connection to the first aggregation point (i.e., the base station) is a shared resource. Thus, availability is not simply a question of coverage. Network capacity is a limitation as well. In other words, the Home Zone service availability is determined by both 3G network coverage and capacity. As a result, operators will be forced to find ways of limiting demand to actually available capacity. Since the cell resource is shared among users within a cell, an operator may limit the number of Home Zone Internet access subscribers within a cell to avoid cell overload. However, setting such a static limit on the maximum number of subscribers per cell is difficult and can lead to under or over utilization of the network at many zones. User behaviour is highly variable (e.g., there are orders of magnitude differences in the traffic demands of light and heavy users, and also the number of non-Home Zone users can vary widely between cells—see, for example, “The Impact and Implications of the Growth in Residential User-to-User Traffic” by Kenjiro Cho, IIJ Kensuke Fukuda, National Institute of Informatics Hiroshi Esaki, The University of Tokyo Akira Kato, The University of Tokyo ACM Sigcomm 2006). This means that quality of service can be impaired in some cells where cell capacity has been reached, while there is spare capacity in other cells. An impaired quality of service means that users experience a slower response and longer download times.